Study of Soft Story Response of Typical Building of NBC

Abstract

Construction of building omitting an infill wall mostly in ground floor and other floors has led a building to face a soft story failure mechanism. This omission of infill wall is for commercial purposes and parking of vehicles in ground floor. In this study, study on the behavior of the structure is done when a soft story happens in different floor levels. A building explained as per NBC 201 and NBC 205 is taken into consideration. Soft story is assigned in all floors to study the responses separately. An equivalent diagonal strut is assigned to the structure to account the consideration of infill wall. Non-linear hinges are assigned to structural members. Different parametric study is performed in terms of displacement, story drift, time period, formation of hinges, performance point, and capacity curve to compare the behavior of the structure. Linear static and non-linear static (Pushover analysis) analysis is performed to evaluate 4 different models. Modal analysis is performed to obtain time period of different models. The time period of bare frame, ground floor soft story, first floor soft story and second floor soft story using modal analysis is 0.65, 0.49, 0.47 and 0.29 respectively. Pushover analysis is performed to obtain pushover curve of different models forming different non-linear hinges in multiple steps of analysis. Step 1, 4, 7 and 10 were analyzed and hinges from basic to collapse prevention has formed. Story drift of bare frame of all story has been compared to the story drift of buildings having soft story in ground, first and second floor. Comparing variation of story drift for ground, first and second floor between bare frame and ground floor soft story model, the values show 13%, 82% and 85%. The variation of same between bare frame and first floor soft story shows 78%, 20%, 81% while the variation between bare frame and second floor soft story shows 97%, 97%, 21%. Additional, a multiplication factor has been introduced to compare the value of factor provided by IS 1893:2002. According to IS 1893:2002, the value should have been 2.5, but the value varies for 3 different cases. It varies from 1 to 1.16.